The waterborne polyurethane dispersions based on polycarbonate diol: Effect of ionic content

doi:10.1016/j.matchemphys.2012.11.057

Materials Chemistry and Physics

Volume 138, Issue 1, 15 February 2013, Pages 277-285

https://doi.org/10.1016/j.matchemphys.2012.11.057 Get rights and content

Abstract

Three water-based polyurethane dispersions (PUD) were synthesized by modified dispersing procedure using polycarbonate diol (PCD), isophorone diisocyanate (IPDI), dimethylolpropionic acid (DMPA), triethylamine (TEA) and ethylenediamine (EDA). The ionic group content in the polyurethane-ionomer structure was varied by changing the amount of the internal emulsifier, DMPA (4.5, 7.5 and 10 wt.% to the prepolymer weight). The expected structures of obtained materials were confirmed by FTIR spectroscopy. The effect of the DMPA content on the thermal properties of polyurethane films was measured by TGA, DTA, DSC and DMTA methods. Increased DMPA amounts result in the higher hard segment contents and in the increase of the weight loss corresponding to the degradation of the hard segments. The reduction of hard segment content led to the elevated temperature of decomposition and to the decrease of the glass transition temperature and thermoplasticity. The atomic force microscopy (AFM), results indicated that phase separation between hard and soft segment of PUD with higher DMPA content is more significant than of PUD with lower DMPA content. The physico-mechanical properties, such as hardness, adhesion test and gloss of the dried films were also determined considering the effect of DMPA content on coating properties.

Graphical abstract

Highlights

► Polyurethane dispersions (PUD) were synthesized from polycarbonate diol. ► The effect of the DMPA content on the thermal properties of PUD films was measured. ► The thermal stability of PUD was increased by decreasing the DMPA content. ► T_g values of PUD were increased by increasing ionic content. ► The PUD with the highest content of DMPA showed more significant phase separation confirmed by AFM results.

Introduction

Water-based polyurethane dispersions (PUD) have gained increasing importance in a range of applications, due to excellent properties such as adhesion to a wide range of substrates, resistance to chemicals, solvents and water, abrasion resistance and flexibility [1]. Water-based polyurethane dispersion show very good mechanical and chemical properties and match the regulatory pressures for low volatile organic compound (VOC) emission. PUDs have numbers applications as flexible coatings for textiles and hard coatings for wood and metallic surfaces.

The continuous reduction in costs and the control of VOC emissions increase the use of water-based resins, motivating the development of polyurethanes (PUs) dispersed in water. These products fulfil many of the requirements related to conventional solvent-born coatings, e.g., low viscosity at high molecular weight and good applicability.

The basic components used to obtain PUD include: long-chain polyol (polyether, polyester or polycarbonate), diisocyanate (aromatic or (cyclo)aliphatic), low molecular weight glycol and/or amine, bis-hydroxycarboxylic acid and neutralization base. In general, an excess of diisocyanate is treated with a linear polyol, bis-hydroxycarboxylic acid and other low-molecular-weight glycol (amine) to form an isocyanate-terminated prepolymer with a segmented structure. In this polymer, the soft segments are formed from long-chain polyol units and hard segments are built-up from diisocyanate, glycol (amine) and bis-hydroxycarboxylic acid.

The polyols used in polyurethane dispersion synthesis are polyether-, polyester-, polycaprolactone- and polycarbonate-origin. The use of individual types of polyol chain and their functionality depends on the purpose of the potential application, e.g.; PU made from polyesters can have slightly elevated strength and oil resistance compared to polyether-based PUs and have been largely used in polyurethane paints as they exhibit outstanding resistance to light and ageing. Polyether polyols are susceptible to light and oxygen when hot, however, they improve water dispersion, and impart chain flexibility [2], [3]. The use of polycarbonate diols (PCD) in PUs and PUD, as compared to other polyols, imparts better hydrolysis resistance, improved ageing and oil resistance, excellent elastomeric properties even at low temperature, improved mechanical properties, good weathering and fungi resistance [4].

Polycarbonate diols used as the soft segment component in polyurethane synthesis are usually produced from dimethylcarbonate or ethylene carbonate and a linear aliphatic diol [5]. The properties of polyurethane dispersions are related to their chemical structure [6], [7] and they are mainly determined by the interactions between the hard and soft segments, and the interactions between the ionic groups [8]. Recent studies demonstrated that the ionic group content, segmented structure, molecular weight of the polyol, the type of chain extender and the hard/soft segment ratio (NCO/OH) determined PUD properties [8]. The properties of the polyurethane dispersions are strongly influenced by the composition and ionic content [9], [10]. The dimethylolpropionic acid (DMPA) containing pendant carboxyl group is one of the most commonly used hydrophilic ionomer, due to the reactivity of its two OH groups. The advantage of using this compound is related to the steric hindrance of the carboxyl group in compared to tartaric acid (TA), so that its interaction with isocyanates is minimized [2].

However, there are still a few studies dealing with the synthesis and characterization of polyurethane dispersions based on polycarbonate diols [4], [8], [9], [10]. Lee et al. [9] synthesized waterborne polyurethane by using various polycarbonate diol with different molecular weight and the internal emulsifier-dimethylolbutyric acid (DMBA), from 2.4 to 11 wt.% (with respect to the prepolymer weight), by a modified dispersing procedure. They concluded that the particle size decreased as the ionic group content of the polyurethane dispersions increased and their properties were also affected by the molecular weight of the polycarbonate diols. Vanesa et al. [4], [8] studied the effects of different NCO/OH molar ratio on the properties of waterborne polyurethane dispersions obtained by the acetone method.

Considering the lack of studies in the existing literature on the influence of the various ionic content on thermal, mechanical and dynamical–mechanical–thermal properties, in the present study, water-based polyurethane dispersions derived from isophorone diisocyanate (IPDI) and polycarbonate diol, were prepared by the modified dispersing method. The ionic groups content in the polyurethane structure was varied by changing the amount of the internal emulsifier-DMPA (4.5, 7.5 and 10 wt.% to the prepolymer weight). The aim of this study was investigation of PUDs' structure–properties relationships. The influence of the ionic groups content on the properties of the polyurethane dispersions was investigated. According to the analyzed references we have concluded that this is the first contribution dealing with the detailed study of the ionic-content influence on the properties of polyurethane dispersions based solely on polycarbonate diol as the soft segment.

Section snippets

Materials

Polycarbonate diol T5652 with a molecular weight of 2000, hydroxyl value 56.3 mg KOH/g, was kindly provided by Asahi Kasei Corporation. The polycarbonate diol is claimed to be produced from 1,6-hexanediol and 1,5-pentanediol by transesterification with ethylene carbonate. The molar ratio of 1,5-pentanediol to 1,6-hexanediol in T5652 is 50:50 and it is liquid at room temperature. Isophorone diisocyanate (IPDI) and dimethylolpropionic acid (DMPA) were supplied by Aldrich. Ethylenediamine (EDA)

Results and discussion

FTIR spectroscopy confirmed all anticipated structures in prepared PUD. Fig. 1a shows the comparative FTIR spectra of polyurethane dispersions with different DMPA content as hard segment content. The assignments of the most characteristic FTIR peaks are given in Table 2. FTIR spectra of samples PUD 1 to PUD 3 feature by the absence of characteristic peak of free NCO groups at 2270 cm⁻¹, that means the full built-up of IPDI into PU dispersions.

The PUD with the increasing of the ionic content in

Conclusions

This paper describes the synthesis and characterization of polyurethane ionomer based on polycarbonate diol varying of the internal emulsifier content. The different DMPA content influenced the intensity and wave number of several FTIR bands of the polyurethanes showing differences in the hard content. DTA thermograms showed segmented structure of the polyurethanes and a distinction between soft and hard segments was obtained. The decrease in the DMPA content produces a decrease in the hard

Acknowledgements

The project was financed by the Ministry of Science and Technological Development of the Republic of Serbia (Projects No. III 45022 and III 45020) and the Grant Agency of the Czech Republic (Czech Science Foundation, project No. P108/10/0195).

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The waterborne polyurethane dispersions based on polycarbonate diol: Effect of ionic content

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Materials

Results and discussion

Conclusions

Acknowledgements

Prog. Org. Coat.

Int. J. Adhes. Adhes.

Prog. Org. Coat.

Prog. Org. Coat.

Prog. Org. Coat.

Polym. Degrad. Stab.

Polym. Test.

Int. J. Adhes. Adhes.

Polym. Degrad. Stab.

Polymer

Prog. Org. Coat.

Polymer

Eur. Polym. J.